The Open Data Acquisition Standard (ODAS) drafted by the new Open Data Acquisition Association establishes a viable software interface definition for PC plug-in (PCPI) data acquisition cards. The standard provides a specification for the five primary subsystems found on most data acquisition boards and is based on Microsoft COM technologies—not on any one vendor’s current software implementation.
The association is made up of leading PC-based data acquisition companies: ComputerBoards, Data Translation, Hewlett-Packard, LABTECH, OMEGA Engineering, and Strawberry Tree. The group is dedicated to developing and maintaining a universal, open standard allowing interoperability between data acquisition hardware and software from multiple vendors.
The ODAS addresses the two choices you have when interacting with PCPI hardware. You can write your own programs using a language such as Visual Basic, C++, or Delphi. Or, you can use a software application such as LabVIEW or HP VEE to create a program that executes in that environment.
Writing your own program is difficult if you plan to use PCPI boards from more than one vendor. Board commands and command structures vary greatly among vendors. And working within the confines of a purchased software application also may be awkward, but for different reasons.
For example, Hewlett-Packard allows each PCPI board vendor to add interface software to HP VEE. If you use VEE, you must deal with a different user interface for each vendor’s cards. As a result, each vendor must maintain compatibility with revisions of the VEE application software.
LABTECH takes another approach. It integrates the interfaces to ensure that you have a consistent interface regardless of which vendor’s PCPI board is used. A separate software layer is written on top of the I/O libraries from each vendor’s application programming interface (API). This approach puts the burden on the application software designers to maintain compatibility with all PCPI vendor’s products and changes.
ODAS fits between the application software program and the PCPI board drivers, providing additional thin layers or shims for each. On the application side, the ODAS manager allows all the installed ODAS drivers to be seen and the proper ones selected.
An ODAS driver combines a hardware-specific device driver and a shim interface layer. Together they provide a standard user interface for the application program. ODAS drivers are Microsoft COM components and can be developed in any programming language.
In the application program, user-defined aliases link logical designations to physical card types. For example, DAC CARD 1 could refer to a ComputerBoards Model PCI-DAS1602. If a different type of board with similar capabilities is used, only the aliases need to be altered and the proper driver installed. The application software will run without change.
In addition, COM provides the infrastructure needed to allow client software on one computer, such as a Visual Basic program, to manipulate a component like an ODAS driver on a remote computer. The COM standard is a mature specification and becoming the ubiquitous object model for developing component software.
Copyright 1999 Nelson Publishing Inc.
January 1999